The electric wires connecting between the Device(s) Under-Test (DUT(s)) and the electronic equipment, which delivers the various electrical stimuli to the DUTs and measure them accordingly, require special attention, in particular when very sensitive devices are involved. Since the DUTs are commonly placed on a special fixture (hereinafter “Test Fixture”), these connecting wires may develop non-negligible Ohmic voltage drop due to the flowing current, as well as leakage to their surroundings. The stringent demands from state-of-the-art electronic device testing, in terms of accuracy, sensitivity and low-leakage current, over a wide range of current and voltage levels, make such connectivity issues both important and challenging.
The most common approach to address these concerns is by using two tri-axial cables (hereinafter “Triax”) per each electronic stimulus, where both sensing the true voltage on the device nodes and minimizing the leakage are important issues. For One of the two cables, the center conductor is the forcing signal, the surrounding cylindrical conducting shell is the guarding signal (“Guard”), driven by the same potential as the forcing signal, but insulated both electrically and physically from it. Finally, the outer metal shell is usually connected to ground potential for safety and also shields from outside noise. Similarly, the center conductor of the second Triax delivers the signal sensed at the device node to the measurement unit, with a similar guarding scheme and outer metal shell. Since the force and sense lines are fully enclosed by their surrounding Guards, all with almost the same potential, the leakage is reduced significantly. Also, connecting the sense line to the DUT assures measurement of the required voltage at the DUT, rather than the forcing signal, possibly affected by Ohmic losses along its connecting line. In other words, the testing instrumentation (hereinafter, the “Tester”) that the Force and Sense lines come from can use the Sense Signal to adjust the Force signal accordingly, and verify that the signal at the DUT end is indeed of proper value.
As this technique is well known and documented in the prior art (for example. Agilent Technologies 4155B/4156B Semiconductor Parameter Analyzer User's Guide General Information, page 2-38), it is obviously beyond the scope of this application. However, even with such two-Triax approach, there is a problem with the final connection within the Test Fixture. As each Triax terminates with a respective connector on the Test Fixture, the final electrical link from this connector to the DUT is implemented with simple wires due to physical constraints (see FIG. 1). Furthermore, to facilitate connectivity to every possible pin of the DUT, a “jumper matrix”, made of plug-in wires linking the signals and their intended destination, is needed. In all, the guarding scheme is practically broken at the connectors that terminate the Triax cables at the Test Fixture and not as close as possible to the DUT. Another problem with the two-Triax scheme is that the Force and Sense lines have to be individually “jumpered” one at a time to the same node. If, by chance, a mistake is made and the Force lines goes to one node of the DUT while the Sense lines goes to another, then that would break the key feedback loop and may cause a voltage on the DUT far different from what was intended. The possibility this error is heightened during tests that require the use of multiple Tester's. (FIG. 2)
The following invention provides a solution to this problem, by different cables, well suited for such task, and an overall simplification of the connectivity scheme. It also introduces a new test fixture mounted as a rotating tray, which can serve as front cover to the electronic equipment as needed. This eliminates the long Triax cables and the separate and remote Test Fixture altogether, while still providing the improved connectivity scheme of the invention.